1. Field of the Invention
The present invention concerns the preparation of isobutane and isohexane containing products. More particularly, the invention relates to a process for the preparation of the those products by disproportionation of an isopentane feedstock in the presence of olefinic or branched-chain paraffinic hydrocarbons and an acid catalyst.
2. Description of the Related Art
Disproportionation of saturated hydrocarbons is a well-known reaction step in the isomerization of normal hydrocarbons to isoparaffins during petroleum refining.
Isoparaffins have a higher octane number than normal paraffins, and are, therefore, preferred components in high octane gasoline products.
During disproportionation reactions, a hydrocarbon feedstock is converted to a hydrocarbon product of higher and lower molecular weight.
Disproportionation of lower paraffinic hydrocarbons to isoparaffinic hydrocarbons is mentioned in U.S. Pat. No. 3,668,269. At the disclosed process, paraffinic hydrocarbon feed is contacted with a solid acidic catalyst comprising a platinum-group metal on a crystalline alumino-silicate. The product obtained thereby contains isoparaffin-hydrocarbons with one more and one less carbon atoms per molecule than the hydrocarbon feed.
Production of isopentane by disproportionation of C.sub.6 alkanes with a catalyst comprising a Group VIII metal and a Group VIB metal is, furthermore, disclosed in U.S. Pat. No. 3,766,292.
It is also known to use AlCl.sub.3 on an aluminum support or alkyl fluoride and BF.sub.3 as promoters in the disproportionation of saturated hydrocarbons.
The general object of this invention is to provide a product being rich in isobutane and isohexane by catalytic disproportionation of isopentane feed.
As mentioned by way of introduction, isoparaffins including isopentane are presently preferred components in high octane gasoline products. However, recent requirements to lower vapour pressure of gasoline, makes it necessary to substitute isoparaffins having a high vapour pressure with components of lower vapour pressure in gasoline.
Isopentane may be disproportionated to isohexanes with a lower vapour pressure and to isobutane, a preferred feedstock in alkylation processes for the production of high octane alkylate gasoline and MTBE; hence, it is desirable to obtain the above substitution of isopentane in gasoline.
It has now been found that disproportionation of isopentane is catalyzed by a strong acid, and the reaction is further promoted by the presence of olefins or higher paraffins, which crack to olefins by influence of a strong acid.